Introduction: To date, a number of simulators ranging from portable equipment to artificial inclines, have been studied. Their efforts were aimed at analysing the effectiveness of existing simulators and to determine the prerequisites necessary to achieve suitable simulators such as Gleitroll bret, Ski power simulator, Ski power home-trainer, the Slide, Pro-Fitter and Skier`s Edge. The aim of this study is to verify the affinity of the "curve movement" structure carried out in a real giant slalom (GS) and on a"new generation" simulator (SS). The simulator used has two breech footboards which can rotate around their longitudinal axis and can be made to vibrate with a frequency variable between 0 to 50 Hz. The athlete is tied with a particularly waist belt from which two cables, which passes through a return pulley, are connected to a traction lever which allows for the dynamic situation found on the ski slopes to be reproduced. Methods: Three different methods have been used: kinematic three-dimensional analysis, analysis of reacting forces at ground level and electromyography (EMG). In the first case, two Canon Movie XM2 videocameras with acquisition frequency of 50 Hz and dedicated software SIMI Motion® were used. The two cameras were positioned at 90 degrees with respect to each other and used simultaneously to record the movements. The data were then processed by computer. Calculations of the principal kinematic parameters, segment movements, angles and angular speed were carried out. To analyse the reaction forces at ground level, SAIR-technology soles with hydro cell sensors having an acquisition frequency of 100 Hz were used. EMG acquisition was made by an electromyographer MEGA with 8 channels and a sample rate of 1000 Hz. In another testing session, vertical and lateral forces acting on the subject`s belt and the insole pressure (force) were recorded (100Hz sample rate) by means of load cells and the PEDAR system respectively. Results: Kinematics parameters reveal some differences on the time history of the knee and ankle joints between the GS and SS. On the SS the joint variations show the same time phase for both legs, whereas in the GS the curves are in a shifted phase. This is due by the difference external constrains affecting the flexion phase. In GS the ski move laterally from each other and this causes the external leg to be much more extended then the internal leg . In SS the feet are fixed to the plates and can only rotate (tilting) according to the frontal plane of the skier. Maximal knee flexion are consistent in the vibration exercise and reach a mean value of 110 deg and 85 deg for external and internal knee, whereas in SS the value are 96 deg and 60 deg respectively. Referring to the distribution of the internal and external reaction forces, the pattern of the curve are in agreement for both situations GS and SS. Mean values of peak force during GS under different vibratory condition and on the SS revealed following: highest value, 2500 N external and 1300 N internal, occurred during the 30 Hz vibration, while in the GS they reach 1400 N and 500 N respectively. In the GS the force curves decrease to a minimum corresponding to the unloading phase between the each turn. In SS situation, on the contrary, the minimum is observed every two maximal flexion, i.e. only when the leg changes his function from external to internal. This is because under the SS, operating only with the vertical cable, there are no centripetal forces allowing the subject to regain his vertical position without great effort, so the leg should still act again the ground to maintain the dynamic equilibrium. The EMG parameters, activation time, RMS amplitude and IEMG integral, showed a high similarity between the two experimental conditions. For the biceps femoris, vastus medialis, and rectus femoris there is a linear tendency to increase the RMS values according to the augmented frequency of vibration. During the slalom the muscles show theirs maximum RMS values. Analogues considerations are founded for IEMG parameter. Comparison of dynamic load conditions, when SS is operating with both lateral and vertical traction cables, shows higher similarity of loading structure with respect to the real skiing situation. Discussion/Conclusion: by means of this study it is confirmed how the concept of specificity of exercise conditions can be evaluated. The similarity of kinematic, kinetic and neuromuscular structure of the movement are established between the slalom and simulator conditions. According to these results it is possible to make new assumption in order to improve the constrains of the simulator (regulation of centripetal force) and make it more useful for training of high level skiers.
© Copyright 2005 International Congress Mountain & Sport. Updating study and research from laboratory to field. 11th-12th November 2005. Rovereto (TN) - Italy. Programme and book of abstracts. Veröffentlicht von Centro Interuniversitario di Ricerca in Bioingegneria e Scienze Motorie. Alle Rechte vorbehalten.